We measured the Shubnikov-de Haas oscillations of the quasi-two-dimensional organic conductor beta-(BEDT-TTF)(2)I-3 under a hydrostatic pressure of 7 kbar. The amplitude of the oscillations was greatly reduced from its ambient pressure value, but the quasi-two-dimensional nature was preserved in spite of a five-fold decrease in T-c. While the fundamental frequency increased by 6.3 %, reflecting the compressibility under pressure, the ratio of the modulation frequency to the fundamental frequency decreased from 9.9 x 10(-3) to 8.3 x 10(-3). Pressure not only compressed the material but also rendered the Fermi surface more two-dimensional.